Broadband wireless is expected to be one of the main drivers of the telecommunications industry. There is a substantial increase in demand for broadband connectivity, with personal broadband being the key growth engine for mobile wireless broadband networks.
Communication in such networks is generally divided between access and backhaul. An access network is the air interface network providing traffic communication between mobile terminals (subscribers) and their associated access points (base stations), while a backhaul network is the air interface network providing traffic communication between the various base stations and a core network. The networks may be arranged to transfer data alone, as in Wi-Fi networks, or may be arranged for triple play services (video, audio and data), typically WiMAX (or other competitive technology, such as 3GPP-LTE). In conventional systems, the access network and the backhaul network each require their own separate transmission equipment, antennas, etc, at great cost to the operator.
One example of a conventional backhaul network is connecting wireless base stations to corresponding core mobile networks (ASN GateWay, AAA servers, etc). The choice of backhaul technology must take into account such parameters as capacity, cost and coverage. Base station backhaul typically is performed via wired infrastructure (e.g., E1/T1 leased lines), or via wireless Point-to-point (PTP) microwave links to each base station, which is expensive to deploy (equipment and installation). In particular, due to the direct, uninterrupted line-of-sight requirements of the wireless backhaul equipment, the backhaul components of conventional base stations require strategic deployment location on high and expensive towers.
In traditional Point-to-Point (PTP) microwave backhaul operating in licensed bands or using unlicensed bands, OFDM (Orthogonal Frequency Division Multiplexing) or single carrier technology (constant power with a fixed modulation scheme) are typically employed. In OFDM, the channel bandwidth is divided into multiple concurrent parallel transmissions on several frequencies. However, during each time slot, there must be transmission over every frequency in the bandwidth. Thus, there is no granulation to permit correction of local interference, and, if there is a problem with transmission on one frequency, the entire transmission can be lost due to lack of frequency diversity, so the Signal to Noise Ratio (SNR) of a link (between two base stations) falls on the entire link.
Mobile WiMAX, as defined in IEEE Standard 802.16e-2005 Standardization for WiMAX, was originally designed to provide mobile broadband access for mobile devices, i.e., broadband wireless data-optimized technology, providing carrier-grade triple play services using a variety of user devices (such as laptops, PDAs, handheld devices, smart phones, etc.). A complete mobile WiMAX Radio Access Network (RAN) requires deployment of massive infrastructure, including base station sites with high towers, base station equipment, antennas, and a separate backhaul network, as described above.
The traditional approach for mobile WiMAX network infrastructure deployment is similar to that of cellular phone networks. The network is based on macro-cell deployment, that is, the base stations, radios and antennas are installed on top of high towers, transmitting at high power, so as to maximize the base station coverage area. In order to optimize the cost, the goal is to minimize the number of sites. This can be achieved by deploying more powerful base station equipment for increasing the cell range (e.g., high power radios, multiple radios on each sector with smart antenna techniques), resulting in more expensive base station equipment. However, for a broadband wireless network deployment, this approach is adequate mainly for the coverage phase, when a relatively small number of subscribers share the cell capacity. As the cell coverage area is large, covering a large number of potential subscribers, additional subscribers in each area can rapidly be blocked due to limited base-station capacity.
There are also known outdoor Wi-Fi networks, deployed mainly according to outdoor Wi-Fi mesh technology. The typical Wi-Fi setup contains one or more Access Points (APs) (which is the equivalent terminology to Base Station in WiMax), having relatively limited range, deployed along telephone poles, street poles, electricity poles and rooftops. Due to the access point unit's smaller coverage range, a large number of access point units are required to cover a given area, typically between 20 to 30 access points per square mile, with wired backhaul at each 3 or 4 hops (known as micro or pico cell deployment). Conventional outdoor Wi-Fi access point units require costly power amplifiers in each unit to extend the capacity in the downlink, but are still limited by link budget in the uplink, due to limited transmission power from mobile station units (such as a laptop, which typically transmits about 20 dbm on a single small integrated antenna) and due to the fact that Wi-Fi utilizes OFDM, where there is no spectral sub-channelization in uplink, which would enable enhancing the link budget. In addition, conventional Wi-Fi networks operate only on unlicensed bands, typically 2.4 GigaHz or 5 GigaHz bands, and suffer from severe interference and difficult radio-planning issues.
Furthermore, in the micro/pico-cell deployment approach of conventional Wi-Fi mesh networks, due to multiple access point nodes in the network, backhauling becomes more complicated and costly. Backhauling each node via wired lines (E1/T1 or DSL) is impractical in a dense deployment of nodes. On the other hand, backhauling each node via traditional wireless PTP microwave links is expensive, due to costly equipment and installation costs. Furthermore, it is not feasible to deploy conventional Wi-Fi backhaul units on telephone poles, street poles, electricity poles, etc., due to the physical dimensions of the backhaul unit and lack of line of sight in urban below-rooftop deployment. In addition, when the network traffic load is increased in multi hop deployment, traffic capacity losses in the backhaul network drastically degrade the overall network performance (capacity and latency), due to incremental loading of cascaded access points in a certain route to the physical line backhaul.
Consequently, there is a long felt need for a wireless mobile broadband network that is relatively low in cost of initial infrastructure (coverage deployment), and also provides high capacity for supporting a large number of broadband data subscribers without high initial deployment cost. In addition, it would be desirable for such a network to support low cost planning, installation and equipment deployment, and to permit relatively easy addition of new access points to the network.